This application is entitled to the benefit of, and incorporates by reference essential subject matter disclosed in PCT Application No. WO 00/63560 filed on Apr. 19, 2000 and French Patent Application No. 99/05146 filed on Apr. 20, 1999.
The present invention relates to a method for mounting and aligning the bearings of the crankshaft of a scroll compressor, to a device for carrying out this method and to a scroll compressor obtained by means of this method.
A scroll compressor is illustrated in longitudinal section in FIG. 1. This compressor comprises a hermetic casing 2, within which are formed a suction chamber 3 provided with an inlet 4 for the gas, and a delivery chamber 5, or pressure chamber, provided with an outlet 6 for the gas.
The suction chamber 3 and delivery chamber 5 are separated by a separating wall 7. Within the suction chamber 3 is mounted an electric motor, the stator 8 and rotor 9 of which are illustrated in the drawing. The rotor 9 is associated with a shaft 10, forming a crankshaft, guided in a lower bearing 12 and in an upper bearing 13 mounted inside the body 14 of the compressor.
The pump intended for ensuring the rise in pressure of the gas consists of two volutes, a fixed volute 15 belonging to the separating wall 7 and a movable volute 16 driven by the end of the crankshaft, this end being eccentric with respect to the crankshaft axis centred on the bearings 12 and 13. This end of the crankshaft is mounted in the rotary part of the compressor by means of a bearing 17. During the orbital movement of the movable part with respect to the fixed part of the compressor, the volume of the pockets in which the gas is trapped decreases, in such a way that the gas is compressed, before escaping via an outlet port 18, on which is mounted a delivery valve 19 allowing compressed gas to pass towards the pressure chamber 5 and preventing gas from passing from this same chamber towards the suction chamber, from the moment when the machine stops.
It should be noted that it is important to ensure that there is exact alignment of the bearings 12 and 13 of the crankshaft and to position the lower bearing axially in order to ensure functional plays between the top of the crankshaft 10 and the end of the bearing driving the movable volute 16 of the scroll and between a counterweight 39 (FIG. 2) integral with the crankshaft 10 and the body 14, on the one hand, and the base of the movable volute 16 of the scroll, on the other hand.
The problem presented can be solved without much difficulty if the stator is mounted in a tube which is itself mounted inside the body of the compressor.
The problem still exists, however, if the stator is inserted directly into the shroud of the compressor, since, in such a case, the geometry of the machine is governed by the casing formed by the shroud.
In some compressors, then, this geometry is liable to change during the manufacture of the compressor. This applies particularly if the body of the compressor comes to bear on the shroud forming the body, and if the body is closed by means of a cap which is welded to the shroud in the vicinity of the bearing face of the body on the shroud. This weld typically deforms the shroud and changes the references.
In such a case, it is expedient to have the possibility of carrying out the alignment of the bearings of the crankshaft, in particular of the bearing for mounting the crankshaft in the body and of the bearing for mounting the crankshaft in the region of the motor, after this weld has been made.
The general object of the invention is to provide a method and a device making it possible to carry out such alignment.
For this purpose, the method to which it relates comprises:
mounting the body of the compressor and the compression elements in the casing of the compressor, with the body or fixed scroll bearing on one end of the shroud of the casing, and then welding a cap to the shroud, the crankshaft being previously or subsequently engaged in a bearing belonging to the movable part of the compression stage and in a bearing belonging to the body, the crankshaft likewise having to be mounted in a lower bearing, itself mounted in a support intended to be fastened to the casing of the compressor,
displacing the free end of the crankshaft in a plurality of directions perpendicular to its axis, in order to take into account the play of the bearing mounted in the body, and then determining the axis of the lower bearing on the basis of the various displacements,
positioning the bearing as a function of this axis, and
fastening the support equipped with the bearing to the casing of the compressor or fastening the bearing to its support previously fastened to the casing of the compressor.
Advantageously, this method involves aligning the bearings when the crankshaft is in a position such that the displacement of the crankshaft in a plane substantially perpendicular to the two parallel planes delimited by the sealing lines between the fixed and movable volutes of the scroll, are parallel to the axis of the crankshaft.
According to one embodiment of the invention, the fastening of the support to the shroud is carried out by welding.
In addition, the support of the bearing comprise at least three radial branches.
According to another configuration, with the compressor being positioned vertically xe2x80x9cupside downxe2x80x9d, this method involves engaging the lower bearing on the crankshaft, exerting a pull on the crankshaft in order to suspend it by a predetermined value, positioning a measuring device, such as a comparator, fastened to a fixed part, such as the casing of the compressor or a support, and bringing the measuring device to bear against the bearing or a piece integral with the bearing, the axis of symmetry of the counterweight of the rotor being approximately perpendicular to a first direction of radial displacement of the bearing. The middle of the stroke in this direction is determined by imparting a to-and-fro movement to the crankshaft, then carrying out the same operation in at least one other direction. The axis of the bearing being obtained by taking into account half the axial stroke along the various directions of displacement.
According to a second possibility, with action being taken on the free end of the crankshaft, the method comprises causing the crankshaft to inscribe a closed or quasi-closed curve by applying a radial force rotating through 360xc2x0 on the end of the crankshaft. This causes the crankshaft to come to bear against the bearing mounted in the body. The centre of gravity of the curve is then determined and the axis of the lower bearing is keyed on this point before fastening to the casing. Advantageously, in such a case, the method comprises causing the crankshaft to rotate about its axis at the same time as the radial force rotating through 360xc2x0 is applied.
Different embodiments of the method are possible.
According to a first embodiment, the method comprises, before the displacement of the crankshaft in order to determine the axis of the lower bearing, engaging on this free end a bearing mounted with a suitable fit in a support, itself mounted with radial play in the shroud with the possibility of being fastened to the latter.
According to a second embodiment, the method comprises determining the axis of the lower bearing by the displacement of the free end of the crankshaft in a plurality of directions perpendicular to its axis, then engaging on the free end of the crankshaft a bearing mounted in a support, itself mounted with radial play in the shroud with the possibility of being fastened to the latter.
According to a third embodiment, the method comprises fastening the bearing support in the casing of the compressor, taking into account the desired distance between the end of the shroud serving for the bearing contact of the body and the support, then, after mounting in the casing of the compressor the various component elements of the latter, carrying out the alignment of the lower bearing with the upper bearing by displacing the bearing within an orifice of larger area which the support comprises, and, after carrying out this alignment, fastening the bearing to its support.
The invention also relates to a device for carrying out the method comprising:
a stand intended for receiving the compressor, and
a mechanism for holding the free end of the crankshaft.
According to one embodiment, this device comprises:
a stand intended for receiving the compressor, the free end of the crankshaft facing outwards,
a table arranged at the end of the stand and comprising two parallel plates associated with means for displacement and for measuring the displacement in two perpendicular directions,
pieces fixed to the plate nearest the compressor and intended for fastening the branches of the lower-bearing support, and
a cap for holding the free end of the crankshaft, the said cap being driven in a longitudinal movement in order to set the axial position of the crankshaft.
The invention also relates to a scroll compressor comprising a casing consisting of a shroud, within which are mounted the body of the compressor and compression elements, with the body or the fixed part of the scroll bearing on one end of the shroud before the latter is closed by the welding of a cap, the crankshaft which drives the movable part of the scroll being engaged in a bearing belonging to the movable part of the compression stage, in a bearing belonging to the body and in a lower bearing, characterized in that the lower bearing is equipped with means for setting its alignment with the bearing belonging to the body.
According to a first embodiment, the bearing is mounted with a suitable fit in a support, and the support is mounted with radial play in the shroud of the casing, and is equipped with means for positioning, for example by screws, before fastening by welding.
According to a second embodiment, the bearing is mounted with radial play in a support, with blocking in the alignment position, for example by screwing, the support being itself of a size fitting that of the interior of the shroud of the casing and being fastened in the latter at a predetermined distance from the end of the shroud serving for the bearing contact of the body or of the fixed part of the scroll.